The present invention relates to an interference measurement apparatus of a high resolution, an interference measurement probe used for such interference measurement apparatus, and an interference measurement control system having an interference measurement apparatus and an interference control apparatus.
A Z-displacement sensor has been generally used as a sensor section for focussing on objective lens in, for example, a precise position control system. A focussing technology of the objective lens is applied to, for example, an auto-focussing mechanism. Among the Z-displacement sensors, an optical lever system has been known as an optical Z-displacement sensor.
FIG. 14 is a perspective view showing an operation principle of the optical lever system. The constitution composed of the components surrounded by the dotted lines is called the Z-displacement sensor (Z sensor).
First, a beam of light from a laser 141 is irradiated onto a objective 143 via a light projection system 142. A reflected light from a objective 143 is incident onto a light receiving section 145 via a magnifying projection optical system 144. With such constitution, a focus point of the optical system is previously adjusted where the point image of the laser beam is formed just on the plane of the objective. When the focal shift occurs, in the light receiving section 145 the image moves in accordance with the amount of defocusing.
Consequently, a feedback control for the sending mechanism of a Z-stage of the objective is performed using a positional shift of a spot image as an error signal, whereby an autofocus mechanism can be realized.
However, an optical system has not been heretofore fabricated in the form of one device, so that an extra optical element must be inserted between the objective lens and the objective. Moreover, since the measurement section measures the position shift of the spot image, there has been a limitation to a resolving power.